after the ingestion of large quantities of fluid, especially when absorption proceeded rapidly. And any cause which obstructs the return of the blood through the splenic vein-such as disease of the liver, heart, or lungs, occasioning an impediment to the flow of the blood through either of those organs-produces an enormous increase in the amount of blood contained in the spleen thus, a well-fed, healthy horse having been kept under the influence of chloroform for half an hour, during which time the respiratory movements were very imperfectly performed, its spleen was found to contain no less than 9000 grains of blood. That the vascular distensibility of the spleen varies greatly in different animals-being much greater in the Ruminants. for example, than in manis a fact that has long been known; but Mr. Gray has added much to our previous information upon this point; and one of the most interesting facts which he has noted in regard to the comparative anatomy of the organ as a whole, is its large size and great distensibility in diving animals, such as the seal and the ornithorhyncus, which are liable to have their respiratory circulation temporarily suspended, but which are not furnished with those arterial plexuses and multiplied venous reservoirs, that enable the cetacea to undergo a prolonged submersion without inconvenience. Thus it is obvious that one of the functions of the spleen is the regulation of the quantity of blood in circulation, since it acts as a diverticulum for the reception of a temporary excess in the whole bulk of the fluid, and also serves as a reservoir to relieve any accumulation which may take place, from whatever cause, in the systemic venous circulation. There is no novelty in this doctrine; but Mr. Gray has furnished much valuable evidence in support of it. One mode of experimenting, however, does not seem to have occurred to him, which would have afforded unexceptionable information as to the degree of vascular distensibility of the spleen in different animals, and would, moreover, have probably furnished interesting results with regard to the conditions of the lacunar circulation-namely, to tie the splenic vein during life, and then to ascertain the amount of blood which the organ contained at different intervals subsequently to the operation, and to investigate the state of its parenchyma, both microscopically and chemically.

The peculiarities in the microscopic characters of the splenic blood are stated by Mr. Gray to be-1st. Considerable variations in the size, form, and colour of the red corpuscles, corresponding with those already described in the corpuscles which he considers to form part of the splenic parenchyma; 2nd. The rare or occasional presence of corpuscle-holding cells, corresponding with those met with in the spleen-pulp; 3rd. The almost constant existence of numerous pigment-granules, or masses, or rod-shaped crystals, these also existing either free, or contained in cells, as in the spleen-pulp; and 4th. The constant existence of a large number of colourless corpuscles, some of which are in the condition of nuclei, whilst others present more or less distinct traces (especially when treated with acetic acid) of an investing cell-wall; both kinds, however, being apparently derived directly from the splenic parenchyma. These peculiarities were constantly found to distinguish the blood of the splenic vein from that returning from any other organ; and no variations were discoverable by the microscope, either in the colour of the blood-discs, the number of coloured granules, or the proportion of the colourless corpuscles, according to the time that had elapsed since the ingestion of food.

The results of the chemical analyses performed by Mr. Gray (with the assistance of Dr. Noad) are tolerably satisfactory as to their general uniformity; at the same time that they present variations which can be frequently referred to certain modifying influences. It is a note-worthy deficiency in the account of these researches, that the mode of analysis adopted by Mr. Gray is not stated. It is well known to all who have attended to this subject, that the proportions of fibrin, corpuscles, albumen, and salts, that may be determined to exist in any given sample of blood, will vary greatly according to the method which has been followed; and there is perhaps none that can be relied on as giving absolutely true results.* Of course, where the same method has been employed throughout (as we presume to have been the case in Mr. Gray's researches), the results admit of mutual comparison; but they cannot be fairly compared

See the writer's Principles of Human Physiology, fourth edition, pp. 149-152.

with those of any other analyst, unless it is known that the like method has been followed by both.

The total amount of solid matter contained in the blood of the splenic vein is affirmed by Mr. Gray to be very considerably less, under ordinary circumstances, not only than that of arterial blood, but also than that of ordinary venous blood, which usually shows some diminution in this respect; this reduction, however, does not take place in all the components of the blood, being usually confined to the crassamentum, whilst the solids of the serum may even undergo an increase. When the question was still further narrowed by the separation of the several components of the blood, the very remarkable result was obtained, that the proportion of red corpuscles in splenic blood does not, under ordinary circumstances, average much above one-half of the proportion contained in arterial or in other venous blood. This reduction far exceeds that which presented itself in Béclard's analyses, the proportion of red corpuscies in splenic blood being stated by him as about four-fifths that of arterial blood, and about nine-tenths that of ordinary venous blood. The discrepancy is probably to be attributed, in part, to the mode in which the blood was obtained; but may be partly accounted for by differences in the conditions of the animals experimented on; for it was found by Mr. Gray, that the greatest reduction takes place at the time of the greatest turgescence of the spleen, -namely, about the period of completion of the digestive process, whilst the amount of change observed at an early period after the ingestion of food is very trifling; and in starved animals, no change whatever is detectible.

The proportion of fibrin contained in the emerging blood of the spleen is generally much larger than that contained either in arterial or in ordinary venous blood; the average of twelve experiments giving 6-4 parts per 1000, which was just double the average for the arterial blood, and one-third more than the average for the ordinary venous blood, of the same animals. Very marked variations presented themselves, however, the maximum being 11.53 per 1000, whilst the minimum was but 2.5 per 1000; and these variations had no perceptible relation to the period of the digestive process. Mr. Gray thinks that the increase of fibrin bears some relation to the diminution of the corpuscles, but his tables by no means bear out this notion; for although in the blood which presented the above-named maximum of fibrin, the corpuscles were reduced from 188-4 to 600, or less than one-third, another sample gave nearly the same proportion (10-88) of fibrin, with a far less reduction in the corpuscles; whilst another sample, with a reduction in the amount of corpuscles from 104-8 to 27.93, or not much more than one-fourth, yielded only 4.31 of fibrin. Mr. Gray states that the blood of ill-fed or starved horses always affords a very considerable proportion of fibrin, as compared with that of well-fed animals; but this assertion is by no means consistent with his own analyses.

The increase in the proportion of albumen in the splenic blood was by no means so remarkable, especially as compared with ordinary venous blood: the average of ten analyses giving 600 parts per 1000, whilst in five of these animals the albumen of the arterial blood averaged 37-2 parts per 1000, and in four others the albumen of ordinary venous blood averaged 54.0 parts. The extremes, however, were much wider apart in the case of splenic blood; the maximum having been 83.3 parts, while the minimum was 35-3 parts. In this last case, which was the one in which the corpuscles were unaltered, there was an absolute diminution of the albumen, the arterial blood having contained 40.9 parts of that constituent. The conditions of this variation have not been made altogether clear by Mr. Gray's researches. He thinks that a marked increase in the amount of albumen is generally concurrent with a diminution in the amount of red corpuscles; but that this is not the case in the latest stages of the digestive process in well-fed animals, the corpuscles being then greatly reduced, while the albumen shows but a very trifling augmentation. The number of analyses appears to us far too small, however, and the individual discrepancies far too great, to admit of any such generalization.

The serum of splenic blood is stated by Mr. Gray to be distinguished by the presence of colouring matters, in sufficient quantity to impart a reddish-brown tinge to the residue left on evaporation, and to the various substances extracted from it; a fact

which harmonizes with the previously-cited results of microscopic examination. He does not consider that the presence of neutral albuminate of soda, which is indicated by the formation of a whitish flocculent precipitate on the addition of about twenty times its own bulk of water, is at all peculiar (as Lehmann supposed) to splenic and hepatic blood; since he found a like deposit, in much greater quantity, in the serum of the arterial and of the jugular blood of the same animals.

The saline constituents of splenic blood do not show any marked peculiarity, either as to quantity or quality, save that the proportion of iron in the crassamentum is much greater than in either arterial or ordinary venous blood. Mr. Gray speaks of its amount as increased; but as the whole crassamentum is largely diminished, we apprehend that the increased percentage of iron does not do more than compensate for this reduction, probably not so much; for whilst, as it seems reasonable to suppose, the increased proportion of iron in the crassamentum is due to the dissolution of red corpuscles in the spleen, a part of the iron thus set free must be imparted to the serum through which the granules of altered hæmatin are diffused.*

Connecting the foregoing results of the examination of the splenic blood with the results derived from the microscopical and chemical examination of the spleen itself, Mr. Gray considers himself to be justified in drawing the following conclusions as to the influence exerted by this organ upon the quality of the blood which passes through it. First, as to the red corpuscles:

"The occasional, and in some animals the constant, occurrence of normal and changing blood-globules in the substance of the pulp, and their partial conversion into coloured pigment granules, or crystalline forms, the chemical analysis of which has shown to be identical with the hæmatin of the blood; the arrangement of the bloodvessels, as admirably adapted to admit of the occurrence of these changes under certain circumstances; the frequency of their occurrence throughout nearly the whole of the vertebrata,-all these facts, I think, are in exact harmony with the results of the analyses of the splenic blood, as far as the diminution of the blood-globules is concerned. They clearly show that, in all animals, under certain circumstances, the spleen modifies the constituents of the blood-discs during their transit through the organ, retaining them for a time in the pulp-tissue, and changing the elements of which they are composed." (p. 356.)

It is, however, only when the vascular turgescence of the spleen is such as to cause an extravasation of blood into its pulp, that the corpuscles are thus melted-down: and thus it is that the process is specially observed to take place as a normal occurrence in well-fed animals, at the time when the digestion of a recent meal is introducing a fresh supply of solid matter into the circulation; and that the blood returns from the spleen with little or no change in this respect, in animals whose blood has been impoverished by starvation. Mr. Gray's hypothesis with regard to the alteration in the proportion of iron, which he considers that the spleen effects in the blood in its passage through it, is vitiated by the uncertainty which attaches to the assumptions on which he bases it. He supposes that the red pulp of the spleen withdraws iron from the blood at certain epochs, to reimpart it to the circulating fluid at other times; and that the unaltered blood-discs of the emerging blood receive an extra charge of this component. The large proportion of iron in the crassamentum of splenic blood, however, seems to us to be readily accounted for by the fact, that this crassamentum does not consist of normal corpuscles alone, but that it is made up of blood-discs in all stages of degeneration, which retain their hæmatin, whilst they part with their other contents; so that an unusually large proportion of hæmatin and its metamorphic derivations will naturally be present, part of it still within cells, but another part probably diffused in the condition of pigment granules. A proportional excess of iron in the crassamentum, moreover, is far from indicating (as we have already pointed out) an absolute excess of iron in the whole mass of splenic blood; so that on neither point do we consider that Mr. Gray's hypothesis can be considered as otherwise than purely speculative.

Mr. Gray considers that the facts which he has collected warrant the conclusion, that

Mr. Gray says (p. 357), that "the blood of the spleen contained in the greater majority of cases a much larger quantity of iron than was found either in the blood entering the gland, or in other venous blood;" but this statement is not justiffed by any of the analyses which he gives.

the colourless elements of the spleen-pulp and of the Malpighian bodies serve as a sinking-fund for albuminous materials, during those conditions of the system in which the supply exceeds the demand; a development of cells and nuclei taking place at the expense of the surplus albumen of the blood during the later stages of the digestive process; and a deliquescence of these lowly-organized forms of tissue occurring in the intervals, whereby the proportion of albumen in the blood which passes through the spleen is augmented. He further supposes that part of the increased amount of albumen usually found in splenic blood, may be derived from the colourless components of the red corpuscles which have uudergone disintegration in the organ. To this source, rather than to any direct change effected by the tissues of the spleen in the blood which passes through it, he is inclined to refer the increase in the proportion of fibrin usually presented by splenic blood; but, as already remarked, there is an entire want of conformity between the two classes of facts, as shown in Mr. Gray's own table. Thus in Table II., No. 10 (p. 157), we find the fibrin raised from 0.78 (arterial) to 10-3 (splenic), whilst the corpuscles exhibited no diminution; whilst in No. 8, in which the corpuscles were reduced from 104-80 (arterial) to 27-93 (splenic), the proportion of fibrin was only raised from 179 to 431.-With regard to the function attributed to the spleen by Professor Kölliker, of specially preparing pigmentary matter for the bile, by the disintegration of blood-corpuscles, Mr. Gray shows that the idea derives no support from fact; since (1) there is no special chemical relation between the colouring matter of the splenic blood and the pigment of bile; (2) the removal of the spleen in animals does not affect the colouring matter of the bile, which is as abundant after as before the operation; whilst (3) the bile-pigment is generated before the development of the splenic vein in the chick. He does not deny, however, that part of the free-colouring-matter of the splenic blood may be changed into bile-pigment; though this, for the reasons just stated, cannot be the special object of the disintegration of blood-corpuscles in the tissue of the spleen, as Kölliker supposed.

Thus, according to Mr. Gray, the Spleen serves to balance alike the quantity and quality of the blood; and is specially adapted for this function by its connexion with that part of the vascular system which is concerned in the introduction of new material into the circulation. This function, however, is so far from being absolutely essential to life, that the complete removal of the organ does not seem to be attended with any injurious consequences; as Mr. Gray has ascertained by his own experiments, which confirm those of many previous inquirers. He does not speak of having observed any symptoms of plethora, such as those noticed by Dobson; but he tells us that two of the cats on which he operated, having been kept for a considerable time, improved much in condition, growing to a much larger size than other uninjured cats of the same age. supposes that the function of the spleen, in so far as this consists in the disintegration of the red corpuscles, and in the increase of the albumen of the blood, is taken on by other parts and organs; since there is usually found to be a slight difference in both these particulars between arterial and ordinary venous blood; while the general hypertrophy of the tissues just noticed as an occasional result of the removal of the spleen, would seem to show that the augmented amount of albumen is stored up in the system generally, when it cannot be received by the spleen.

And he

"Although these elements," he remarks, "cannot as readily, under the above conditions, be restored to the blood, as if the spleen had retained them, to be used at every occasion or requirement of the animal, still their removal from this fluid, where they exist in great excess, serves to effectually prevent the inconvenience which a too great accumulation of them in the blood would certainly occasion." (p. 372.)

Fully admitting the force of all the facts upon which Mr. Gray has attempted to build up his physiological induction, we must yet confess that he does not appear to us to have by any means succeeded in affording a complete solution of this obscure but interesting problem. There is a difficulty which does not seem to have presented itself to him, arising out of the very magnitude of those alterations in the constituents of the blood, of which he affirms that the spleen is the instrument. In Table IX. (p. 177),

which gives the average results of 111 analyses of the aortic, jugular, and splenic blood of the horse, we find the following to be the amounts of water and of solid constituents in each respectively:

Thus, whilst arterial blood undergoes a trifling reduction in the amount of its solids, during its passage through the capillaries of the general system, the blood which is transmitted to the spleen loses, on the average, 40-67 parts, or nearly one-fifth. And since, in many of the experiments, the loss was very trifling, it must have been far more than this in a large number of instances, as, for example, in No. 8 of Table II., in which the albumen, fibrin, and red corpuscles of aortic blood amounted to 145.85, whilst the same components of the splenic blood amounted only to 73-47; the difference thus being 72.38, or nearly one-half. Now the question which we affirm to be altogether unsolved by Mr. Gray's researches, and to be altogether passed by in his physiological conclusions, is two-fold:-1. What becomes of all the solid matter of the blood, which is thus apparently kept back by the spleen ?-and 2. How is it that this reduction in the amount of solid matter does not produce a greater effect upon the general mass of the solid constituents of the blood? We know well, that at the ordinary rate of the circulation, the whole amount of blood in the spleen must be renewed many times in the course of a single minute; and all the blood of the body must be submitted to the same operation many times in an hour. If, then, the spleen keep back one-fifth of the solid contents of every pound of blood that passes through it, the organ must soon draw into itself nearly the whole mass of albumen, fibrin, and corpuscles contained in the circulating current; and the blood must be impoverished in a corresponding degree. Our readers will easily apprehend our meaning, if they will call to mind the process by which a large receiver may have its air exhausted by a very small pump, provided that the working of this pump be kept up for a sufficient length of time. Now in this case, all the air which has been drawn from the receiver by the pump, is discharged above the piston as fast as it enters beneath; and consequently there is no accumulation. But in the case of the spleen, there is no such outlet; no means can be traced whereby the withdrawn materials can be disposed of through any other channel; and we seem reduced to the inference, that they are solely, or at least chiefly, applied to the augmentation of the substance of the organ itself. But although this does undergo a certain increase, the amount of such increase is as nothing, compared to that which must result from the retention of one-fifth of all the solid matter of the blood flowing through the spleen at the ordinary rate. And, conversely, the amount of reduction in the solid constituents of the whole mass of blood, by the instrumentality of the spleen, is so small as to be inappreciable; instead of immediately manifesting itself, as it must have done, if the current flowing through the spleen at the ordinary rate, even for a limited time, had suffered a deprivation of one-fifth of its solid constituents. We cannot ourselves perceive any other escape from this dilemma, than by the assumption,-which we admit to be purely hypothetical, but which seems to us to be the only hypothesis that will at all meet the facts of the case, that a large part of the current of blood through the spleen is retarded, almost stagnated, at the time when the organ is in fullest action. And if we seek for a cause for such stagnation, we think that one may possibly be found in the increase of pressure within the tributaries of the vena portæ, arising from the absorption of a large quantity of new alimentary material into the mesenteric vein. If that pressure should so augment as to antagonise (or nearly so) the pressure within the splenic artery, a stagnation of the blood-current in the venous reservoirs of the spleen will be the consequence; and the increased pressure will, at the same time, give rise to the escape of red corpuscles from the lacunar system of the spleen into its parenchyma, which Mr. Gray affirms to be a normal phenomenon in well-fed animals. The wellknown fact that the splenic vein is destitute of valves, seems to us to add some weight to this hypothesis; since an excess of vis à fronte over the vis à tergo may cause not only a stagnation of blood in the veins of the spleen, but may even permit a reflux into